Ophthalmoscopes having laser devices are frequently used for the observation and treatment of eyes. Therein, photocoagulation represents an important method of treatment wherein the fundus of the eye, also referred to as fundus, is coagulated or sclerosed. In order to successfully perform such a treatment it is necessary to position a therapeutic laser beam exactly on the region to be treated. Moreover, an effect of a laser treatment on a treated tissue in the eye has to be controlled and verified.
To this end, the eye to be treated is usually illuminated with visible light during laser therapy. This has the advantage that under visible (white) light a physiological effect of the laser treatment, which as a rule becomes manifest in the form of bleaching of the irradiated tissue, is particularly distinctly visible. In particular, even before laser treatment a test laser irradiation of the eye is therefore experimentally carried out in uncritical regions of the eye in order to perform, under white light illumination, a determination of optimum irradiation duration, irradiation intensity and further parameters.
However, most patients find illumination of the eye with visible light to be dazzling and extremely unpleasant so that the patients concerned often react to the illumination with instinctive ocular movements. These ocular movements considerably complicate observing as well as acquiring an image of the eye. The ocular movements have a particularly adverse effect on the accuracy with which laser irradiation can be applied to a desired region to be treated, thus causing a considerable risk of unintended irradiation of a sensitive region of the eye. In addition, ocular movements as a rule require new positioning of a laser beam, which can result in a considerable extension of treatment duration, in particular if a great number of regions of the eye have to be irradiated individually.
As a result, it is customary to place a contact glass onto the cornea of the eye and in this way to mechanically suppress said ocular movements. However, this leads to irritations of the eye, and as a rule is feasible under local anesthetic only.